Containers for storing hydrocarbons or various chemicals or pipes for transporting these materials include, for example, bottles for chemicals, fuel tanks for automobiles or small size engines, fuel pipes, etc. Most of metals or glass conventionally used as raw materials of these members have been now replaced with a plastic material as an alternate material therefor. The plastic material has advantages such as a light weight, no need of rust-proof treatment, less occurrence of cracks and a high degree of freedom of a shape, etc., as compared to the metals or glass.
In most of the above applications, a high-density polyethylene (hereinafter occasionally referred to merely as “HDPE”) has been used as raw materials of the containers or pipes. The HDPE is excellent in mechanical strength, moldability and economical efficiency. However, the HDPE has such a problem that contents stored in a container made of the HDPE are likely to be permeated through a wall of the HDPE container and dispersed or scattered in atmospheric air. In recent years, regulations against permeation of gasoline through gasoline tanks made of a resin and peripheral members thereof have become much stricter year by year from the viewpoint of avoiding environmental pollution, so that the existing HDPE containers have failed to comply with such stricter regulations. As a result, there is an increasing demand for techniques of enhancing a gas-barrier property of these products.
As a method of enhancing a fuel barrier property of an HDPE container, there is known the method of treating an inner surface of the HDPE container with flon or sulfone (for example, refer to Patent Document 1). In addition, there is known the method of forming an HDPE container having a multilayer wall structure which include an intermediate layer made of a barrier resin such as an ethylene-vinyl alcohol copolymer resin (hereinafter occasionally referred to merely as “EVOH”) (for example, refer to Patent Documents 2 and 3). Further, in order to enhance a fuel barrier property of an HDPE container, there is known the method of producing a single-layer container, from a composition prepared by blending HDPE and a polyamide resin such as nylon 6, 66 or EVOH together with an adhesive resin (for example, refer to Patent Documents 4 and 5). Furthermore, there is also disclosed the method in which poly-m-xylylene adipamide (hereinafter occasionally referred to merely as “N-MXD6”) having a more excellent barrier property than nylon 6, 66 is used in the above blended resin single-layer container (for example, refer to Patent Documents 6 and 7).